docs: def get_ratefactor(self, base, code):
          """
          Return the Decimal currency exchange rate factor of 'code' compared to 1 'base' unit, or RuntimeError
          Yahoo currently uses USD as base currency, but here we detect it with get_baserate
          """
          raise RuntimeError("%s Deprecated: API withdrawn in February 2018" % self.name)
          try:
              rate = self.get_rate(code)
          except RuntimeError:
              # fallback
              return self.get_singlerate(base, code)
  
          self.check_ratebase(rate)
          ratefactor = Decimal(rate['price'])
  
          if base == self.base:
              return ratefactor
          else:
              return self.ratechangebase(ratefactor, self.base, base)